This is the most common cause of painless bloody discharge from the nipple in a woman of reproductive age. It is a benign tumor and there are no characteristic radiologic/mammographic changes.
Ugh when you do it in uworld, write it down but still miss it.
Anyway going over other answers (pathoma):
Fibrocystic changes of the breast --> benign, usually no discharge with this and you will usually have a lumpy breast or something palpable and it is hormone mediated.
Pagets disease of the breast --> extension of ductal carcinoma in situ to lactiferous ducts and skin of nipple producing rash, so you see skin changes. No skin changes mentionedh ere.
Prolactinoma --> gallactorhea not blood tinged
So per UW intraductal papilloma is a proliferation of papillary cels in a cyst wall or duct that may cause focal atypia - IT IS THE MOST COMMON CAUSE OF BLOODY NIPPLE DISCHARGE AND BREASTS WITHOUT BREAST MASS OR SKIN CHANGES
compare this to papillary carcinoma where you also have nipple discharge but you would see it in a post menopausal women.